1. Field of the Invention
This invention relates to a serial data communication system using serial data for half-duplex communication.
2. Description of the Prior Art
The data communication systems may be, as well known, divided into categories, namely the parallel and serial types. From the point of view of the transmission speed, the parallel communication is, of course, preferable. But, because of its necessity of an equal number of communication lines to the number of bits of data to be transmitted, it is inferior in cost advantage to the serial communication.
Also, in performing the serial communication, which of the full duplex and half-duplex communication methods is chosen is determined by taking into account the various factors such as cost and kinds of data to be transmitted. Most of the ordinary communication control systems employ the half-duplex communication method.
It has been customary that even this serial half-duplex communication system necessitates at least one data line and at least two busy lines which let one station know the operative position of a transmitter-receiver of the other station.
Yet, to realize a communication system having a great number of microprocessors, it is desired to reduce the required total number of lines thus simplifying the structure of construction.